The Biochemical Oxygen Demand (BOD) test is a commonly used test in the waste water management field for determining the amount of oxygen depletion that a sample will exert over a given period of time. Thus, the BOD of a waste sample is a measure of its strength and can be used to assess the impact of the waste on a receiving body of water. A standard BOD test involves measuring the initial dissolved oxygen (DO) concentration of a sample with specified volume, and then measuring it again at a later time, generally 5 days later. This information is then used to calculate the amount of oxygen depletion that occurred relative to the sample.
Several prior art references exist which disclose apparatuses and methods for determining oxygen rate consumption or biochemical oxygen demand in continuous flow systems or currents. For example, U.S. Pat. No. 3,374,065, issued to Suzuki, discloses an apparatus for continuously detecting and estimating BOD values in an existing source such as a drainage or river. The apparatus comprises a tube container for testing, means for injecting the sample material into the container, means for injecting a non-organic acid into the container to form a mixture, means for mixing and heating the mixture, means for detecting a low pH which causes the non-organic acid injecting means to close, means for injecting an alkaline and showing the increase in pH, and measuring means to determine the BOD.
U.S. Pat. No. 3,731,522, issued to Mikesell, describes a method and apparatus for determining oxygen rate consumption in sewage. The apparatus comprises an airtight container having an inlet and outlet, pump means for circulating sewage through the container at a constant flow rate, and sensing means for measuring the amount of dissolved oxygen in the sewage at both the inlet and outlet.
Another apparatus and method for determining oxygen rate consumption in a continuous current is described in U.S. Pat. No. 5,017,496 issued to Klapwijk et al. The Klapwijk et al. patent discloses a method comprising the steps of 1) measuring the oxygen content of a sample by passing it in a first direction past a predetermined measurement location and taking a first measurement before the continuous flow enters a given chamber and 2) reversing the continuous flow past the predetermined measurement location in a second direction and taking a second measurement after the continuous process flow has resided in the chamber.
U.S. Pat. No. 5,025,927, issued to Garg, discloses a respirometer apparatus for determining the BOD of less dilute wastewater samples than those used in standard BOD test procedures. The preferred embodiment includes a chamber having walls formed from an oxygen permeable membrane and a frame structure. Two sheets of the membrane are heat-sealed to the frame structure leaving a collapsible opening to communicate with the chamber's interior. The frame structure comprises a base plate and cover plate which are held apart from one another by supports. Inlet and outlet holes are provided in the cover and base plates to accommodate the BOD measurements of continuous flow systems.
Other prior art references disclose systems for measuring the DO and BOD of non-continuous flow liquid samples. For example, U.S. Pat. No. 3,635,564, issued to Zuckerman et al., discloses a system for measuring the organic content of water using a refractometer. Also, U.S. Pat. No. 4,244,695, issued to Melzer et al., discloses a method for quantitatively determining the total oxygen demand of water containing oxidizable matter by continuous evaporation of the water in the presence of oxygen at a temperature of about 900.degree. C.
All of the previously described references fail to disclose an automated system for testing the DO and BOD values of multiple samples. However, several automated test systems are known in various fields of art. For example, U.S. Pat. No. 5,260,872, issued to Copeland et al., describes an automated testing system which includes a robotic arm as well as a programmable computer for functions such as controlling, dispensing, mixing, moving operations, and recording. This reference is directed to an automated system for quality testing samples for a blood-clot dissolving product. Computer software is programmed to provide all of the machine control functions including robotic arm functions, pipetting functions, and the collection and filing of resulting data.
Finally, Applicant is aware of one automated BOD analyzer produced by Skalar, Inc., located in the Netherlands. Skalar's robotic analyzer includes a computer-controlled robotic manipulator system. Samples are loaded on a transport rack which is moved via a rail system to manipulators which then perform a series of tasks on the samples. A series of measuring instruments interface with the robotic manipulator system to measure various parameters. The computer then calculates and displays results.
Although Skalar's automated instrument does perform DO/BOD determinations, Skalar's system does not possess the ability to utilize multiple vendors' DO probes and meters. In addition, Skalar's automated instrument does not possess the ability to utilize multiple probes or rinse the probes between rows of samples without using a dedicated wash area.
Accordingly, there is a need for an automated DO and BOD analyzer which increases the analytical speed for determining DO and BOD values while making use of the analyst's existing equipment, e.g., DO meters and BOD bottles already in inventory.